1. Field of the Invention
The present invention relates to an ink jet printer for printing text, symbols, and images by ejecting ink drops from a plurality of ink nozzles to a printing medium. More specifically, the present invention relates to an ink jet printer control method for efficiently preventing ink clogging of the ink nozzles.
2. Description of the Related Art
Various methods have been proposed and used for ejecting ink from the ink nozzles of an ink jet printer. These include: using a piezoelectric element as taught in Japanese Examined Patent Application (kokoku) 2-51734; using a heating element to heat the ink as taught in Japanese Examined Patent Application (kokoku) 61-59911; and using an electrostatic actuator to vibrate a diaphragm by means of electrostatic force as taught in Japanese Unexamined Patent Application (kokai) 7-81088.
Generally speaking, an ink jet printer generates print data in memory from a print data (image) signal, and then selectively drives the pressure generating device or actuator, such as the piezoelectric element, heating element, or electrostatic actuator, adjacent to the ink nozzles based on the print data in memory to print to the printing medium.
A problem common to each of these ink jet printers is that if the ink drops are not ejected from the ink nozzles for a certain amount of time, the water or other solvent in the ink evaporates. This increases the viscosity of ink near the ink nozzles.
When ink viscosity rises near an ink nozzle, the ink nozzle clogs. This prevents ink ejection during printing, or prevents ink drops from being ejected at the normal speed or volume. The ink nozzles are also refilled with ink more slowly when the ink viscosity rises. Ink refilling is thus unable to keep up with ink ejection, bubbles become mixed with the ink, and ink drops may not be ejected as needed.
A common technique used to prevent this in modern ink jet printers is to cover the ink nozzles with a cap when not printing. This prevents the ink nozzles from drying and thus prevents an increase in ink viscosity near the ink nozzles.
Other methods have also been developed to maintain and restore printer performance by preventively ejecting a small volume of ink from all of the ink nozzles at regular intervals between printing operations as a means of preventing ink clogging near the nozzles.
Japanese Examined Patent Application (kokoku) 6-39163 teaches a recovery method wherein the frequency used to drive the ink jet head for preventive ink ejection is set lower than the highest drive frequency used for printing text and images. When ink viscosity has increased in the ink nozzles, this makes it possible to reliably expel high viscosity ink from the ink nozzles without pulling bubbles from the ink nozzles into the ink path.
Yet another method for preventing ink nozzle clogging as a result of dried ink near the ink nozzles is taught in Japanese Unexamined Patent Application (kokai) 56-129177 and 9-30007. This non-discharging nozzle recovery method prevents clogging by using a signal generator to produce a resonance frequency in the ink jet head when printing is not in progress as a means of stimulating and vibrating the ink meniscus, thereby preventing nozzle clogging as a result of ink drying.
Some of the problems unresolved by the above-noted clogging prevention methods are described below.
First, when the ink meniscus is vibrated without ejecting ink drops from the nozzle in the above non-discharging method, the process must be performed when the ink jet head is stopped. This means that if this recovery method is performed frequently during printing, printing must be interrupted each time and printing speed therefore drops.
Furthermore, this non-discharging method does not expel the increased-viscosity ink from the ink nozzles. This means that over a period of time the viscosity of ink increases not only around the ink nozzle orifice but inside the ink supply path upstream from the ink nozzles, and the problem of ink nozzle clogging by increased-viscosity ink is not solved. Therefore, this non-discharging recovery method may not be effective as a means of reliably solving the problem of ink jet head clogging after the printer has been stopped for a long period of time.
On the other hand, while methods that discharge increased-viscosity ink from the ink nozzles physically expel the ink from the nozzles as part of the preventive discharge recovery process, ink that has not increased in viscosity is also expelled at same time. The problem here is the unnecessary consumption of ink not used for actual printing.
Second, even when the time interval between the preventive ink ejection and the actual start of printing is short it may still be sufficient for a film to form on the nozzles. This is the more likely to happen, as the distance between the preventive ink ejection position and the print start position increases. Such film prevents ink droplets from being ejected at normal speed and/or volume.
Third, in the prior art employing the non-discharging method, varying voltages are applied simultaneously to first and second nozzles during normal printing. The first nozzles are those that, in accordance with the print data, eject a droplet onto the printing medium. The second nozzles are those that, in accordance with the print data, do not eject droplets, but are driven so as to vibrate the ink meniscus without ejecting ink droplets. The necessity of applying varying voltages (not including 0 V) at the same time to a head driver requires a complicated circuit structure.
Therefore, it is an object of the present invention to overcome the aforementioned problems.
It is therefore an object of our invention to provide an ink jet printer control method whereby non-discharge driving the ink jet head nozzles can be accomplished without incurring a drop in printing speed.
A further object of our invention is to provide an ink jet printer control method whereby unnecessary ink consumption can be suppressed, and ink nozzle clogging can be reliably resolved regardless of how long the printer has been stopped.
To achieve the above object, an ink jet printer control method according to our invention accomplishes a non-discharge driving operation while the ink jet head is being moved relative to the printing medium by a carriage or other moving mechanism prior to printing. The ink jet printer has an ink jet head with a plurality of ink nozzles for discharging ink drops, a pressure generating device or actuator disposed corresponding to said ink nozzles for pressurizing ink inside each ink nozzle, and a moving mechanism for moving the ink jet head relative to the printing medium. This non-discharge driving operation is accomplished by the pressure generating device or actuator micro-vibrating an ink meniscus at each ink nozzle.
With the control method of our invention the non-discharge driving operation is accomplished prior to the start of actual printing while the ink jet head is moving to the printing position. It is therefore not necessary to delay the printing operation, and ink nozzle clogging can be prevented by this non-discharge driving operation without incurring a drop in printing speed.
When the ink jet head is stopped without printing for a long time, it is desirable to use a preventive discharge operation to discharge ink drops not used for printing as a means of reliably avoiding ink nozzle clogging when printing resumes. However, constantly performing this preventive discharge operation is not desirable because of the increase in unnecessary ink consumption.
It is therefore desirable to measure a time (Tk) elapsed since the last non-discharge driving operation, a time (Tf) elapsed since the last preventive discharging operation, and then selectively perform either one of the non-discharge driving operation and preventive discharge operation based on these times Tk and Tf.
In a typical ink jet printer a time (Tt) in a non-printing state in which printing does not occur is also monitored and the ink nozzles are capped when elapsed time Tt is more than or equal to a specific period.
Yet further preferably in this case a time (KJ) elapsed with the ink nozzles capped is also monitored. A head cleaning operation for pulling ink from the ink nozzles is then performed when at a start of printing time KJ is more than or equal to a specific period. If time KJ is less than this specific period, the preventive discharge operation is performed.
A further control method according to our invention is for an ink jet printer having an ink jet head with a plurality of ink nozzles for discharging ink drops, and a pressure generating device or actuator disposed corresponding to said ink nozzles for pressurizing ink inside each ink nozzle. The pressure generating device or actuator accomplishes a non-discharge driving operation by micro-vibrating an ink meniscus at each ink nozzle, and a preventive discharge operation for discharging an ink drop with no relation to a printing operation from each ink nozzle. This control method monitors a time (Tk) elapsed since a non-discharge driving operation, a time (Tf) elapsed since a preventive discharging operation, and prior to printing performs either one of a non-discharge driving operation and preventive discharge operation based on times Tk and Tf.
In this case two elapsed times are used so that when the printer was stopped without printing for a short time the non-discharge driving operation is performed, but if the non-printing time was long, the preventive discharge operation is performed. It is therefore possible to reliably prevent nozzle clogging regardless of how long the printer did not print. Unnecessary consumption of ink not used for printing can therefore be suppressed because preventive discharging is not used when non-discharge driving is sufficient to resolve ink nozzle clogging.
In a typical ink jet printer a time (Tt) in a non-printing state in which printing does not occur is monitored. In this case the ink nozzles are capped when elapsed time Tt is more than or equal to a specific period.
It is further preferable in this case to also monitor time (KJ) elapsed with the ink nozzles capped. When at a start of printing time KJ is more than or equal to a specific period, head cleaning for drawing ink from the ink nozzles is performed, but if time KJ is less than this specific period preventive discharging is preferably used to prevent nozzle clogging.
The control method of the present invention can also be provided as a control program executable by a printer controller, and can be provided by a data storage medium on which the control program is recorded. Storage media and devices that can be used for this data storage medium of the invention include: memory, Compact Discs, particularly CD-ROM media; floppy disks; hard disks; magneto-optical disks; DVD media such as DVD-ROM discs; and magnetic tape. Furthermore, these media can be used to supply this control program to existing printers. Yet further, the program can be made available on a World Wide Web (WWW) site from which users can download the program for use with an existing printer.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the. following description and claims taken in conjunction with the accompanying drawings.